Heating furnace



FIG. 1 is a top, front and right side perspective view of a heating furnace showing our new design;

FIG. 2 is a bottom, rear and left side perspective view thereof;

FIG. 3 is a front elevational view thereof;

FIG. 4 is a rear elevational view thereof;

FIG. 5 is a left side view thereof;

FIG. 6 is a right side view thereof;

FIG. 7 is a top plan view thereof; and,

FIG. 8 is a bottom plan view thereof.

The broken lines in the drawings illustrate portions of the heating furnace which form no part of the claimed design. 

CLAIM The ornamental design for a heating furnace, as shown and described. 